U.S. Pat. No. 4,142,748, assigned to the present applicant, disclosed a privacy lock arrangement for door latch assemblies which allows an internal door latch to be snibbed on a first side to lock the latch against entry from the other side, but to be automatically released by simple rotation of the handle at the first side. Privacy lock arrangements in general ensure privacy for the occupant of a room against unexpected entry and are widely used on bathroom, toilet and bedroom doors. The particular arrangement of U.S. Pat. No. 4,142,748 includes a pair of rotary members which interengage with one another so that they can rotate independently through a limited angle of rotation only. A pivoted snib member has a first dog engageable with one of the rotary members to positively lock it against rotation and a second dog which engages the other rotary member in such a way that the relative rotation of the rotary members is effective to move the snib member out of its engagement with the locked rotary member.
The arrangement of U.S. Pat. No. 4,142,748 has the attraction that it may be provided as an adaptor assembly between a backing plate and an escutcheon and therefore does not require modification of the handle, but is also a relatively complex mechanism to manufacture.
Earlier privacy lock arrangements are to be found, for example, in U.S. Pat. No. 3,471,190, and in British patents 861002 and 1159161.
A variation of the arrangement of U.S. Pat. No. 4,142,748 is disclosed in the present applicant's co-pending Australian patent application 19655/92. In that case, the engagement between the releasing rotary member and the snib is by way of a lateral pin on the snib which projects parallel to the main spindle axis and is received in a V-shaped cut-out in a head portion of the rotary member.
In the present applicant's international patent publication WO9310324, respective first and second rotary members include respective notches which are disposed mutually adjacent when the rotary members are at a predetermined relative position, to both receive a commentary lug on a snib member. One of the notches and the lug effect snibbing of the first rotary member while the other notch is effective as camming means during mutual rotation to act on the lug to move the snib member to its freeing position. The snib member is again a pivoted component exposed through the rim of the backing plate for being set against an indexing spring.
Related background art cited in WO9310324 included WO90/15210, U.S. Pat. No. 3,800,573 and U.S. Pat. No. 5,123,682.
It is an object of the invention to provide on one hand, a novel snib mechanism and, on the other, a door lock mechanism incorporating same.